Eloquent: Romney explained yesterday how Obama has either failed to solve the nation’s problems, or made them worse. Photo: AP

‘This election matters” was the theme Mitt Romney invoked time and again yesterday in the most important speech he’s given since the Republican convention — a confident, well-conceived and tough-minded address that he should have delivered at the convention.

But he hadn’t yet found the sweet spot then. He was struggling in that convention speech to combine a positive, nonideological message with a passionate case for the electoral removal of a sitting president.

He found that sweet spot at the first debate on Oct. 4 and has stayed there since. Yesterday, in Ames, Iowa, he showed just how much he has changed for the better as a candidate, a rhetorician — and a salesman who has to close the sale over the next 10 days.

He needs the remaining undecided voters to believe him that “this election matters,” because as the race heads into its final days, Romney’s greatest enemy is not President Obama, but political entropy.

Bouncing a sitting president requires conscious action, a national decision to redirect the country’s course. This cuts against the grain, and that’s why incumbents have a natural advantage.

Late-deciding voters might just figure things in the country are disappointing but endemic, the result of causes beyond Obama’s control. They might figure he did the best he could and Romney can do no better, and so it might be less risky just to keep things as they are.

Yesterday, Romney began simply by asking, “Where are the 9 million more jobs that President Obama promised his stimulus would have created by now?” He answered: “They are in China, Mexico and Canada and in countries that have made themselves more attractive for entrepreneurs and business and investment, even as President Obama’s policies have made it less attractive for them here.”

That’s the deep core of the Romney campaign right there — but pushing that message won’t get the job done on its own. Indeed, he went on to say that the election is about more, and that’s why it matters so much — particularly to constituencies he wishes to win over.

“It matters to the senior,” Romney said, “who needs to get an appointment with a medical specialist but is told by one receptionist after another that the doctor isn’t taking any new Medicare patients, because Medicare has been slashed to pay for ObamaCare.”

“It matters” to those who do have a job, but whose working circumstances have deteriorated, like “the man from Waukesha, Wis., I spoke with several days ago. In what were supposed to be his best work years, he used to have a job at $25 an hour with benefits and now has one at $8 an hour, without benefits.”

He spoke to those entering adulthood in a condition of indebtedness that is not only personal but national: “It matters to the college student, graduating this spring, with $10,000 to $20,000 in student debt, who now learns that she also will be paying for $50,000 in government debt, a burden that will put the American Dream beyond her reach.”

Obama’s beholdenness to Big Labor matters to “the child in a failing school, unable to go to the school of his parent’s choosing, because the teachers union that funds the president’s campaign opposes school choice.”

The president, said Romney, has either failed to solve or worsened the problems facing these Americans. He argues that he inherited a bad situation — but, said Romney, “a troubled economy is not all that President Obama inherited. He inherited the greatest nation in the history of the earth,” made up of people who rise to the occasion and surmount their difficulties.

And yet, despite that positive inheritance, “President Obama did not repair our economy, he did not save Medicare and Social Security, he did not tame the spending and borrowing, he did not reach across the aisle to bring us together.”

This is the pithiest, most engaged argument Romney has presented for change.

Achieving change, he said, “requires that we put aside the small and the petty, and demand the scale of change we deserve: We need real change, big change. Our campaign is about that kind of change — confronting the problems that politicians have avoided for over a decade, revitalizing our competitive economy, modernizing our education, restoring our founding principles.”

The speech presented its listeners with a binary choice: Obama as the candidate of the status quo, Romney as the candidate of the future. If Romney can hammer this home until Nov. 6 as effectively as he did in Iowa yesterday, he’ll be our next president.